Astrophysics SL – Flashcards
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order of solar system
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mercury venus earth mars (asteroid belt) jupiter saturn uranus neptune
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stellar cluster
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grouping of large stars that have gravitational interaction/attraction with each other and are relatively close to one another
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binary star
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two stars orbiting a common centre
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black dwarf
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the remnant of white dwarf after it has cooled down very low luminosity
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black hole
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a singularity in space time the end result of the revolution of a very massive star
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cepheid variable
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a star of variable luminosity with well-defined period the period is related to the absolute luminosity of the star and so can be used to estimate the distance to the star
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constellation
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a group of stars in a recognizable pattern that appear to be near each other in space when observed from the earth
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dark matter
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matter that is too cold to radiate its existence is inferred from techniques other than direct visual observation
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galaxy
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collection of very large number of stars mutually attracting one another through the gravitational force and staying together
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main-sequence star
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a normal star that is undergoing nuclear fusion of hydrogen to helium
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neutron star
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the end result of the explosion of a red supergiant a very small star with high density star consist almost entirely of neutrons, hence its name
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planetary nebula
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the ejected envelope of a red giant star
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red giant
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a main-sequence star evolves into a red giant there are nuclear reactions involving the fusion of helium into heavier elements
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white dwarf
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the end result of the explosion of a red giant small, dense star in which no nuclear reactions take place although hot, small size gives very low luminosity
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luminosity
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power radiated by a star
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apparent brightness
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received power per unit area
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parallax
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change in position of a star in the sky at times six months apart
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Wien displacement law
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higher the temperature, the lower the wavelengths at which most of the energy is radiated
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standard candles
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a star of known luminosity *period can be used to find luminosity, which can then find apparent brightness, which finds distance. hence, relative distance can be measured using standard candles.
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Chandrasekhar limit
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mass at which electron degeneracy pressure prevents the further collapse of the core, star will become a stable white dwarf
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Oppenheimer-Volkoff limit
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mass at which star can maintain stability and become a neutron star
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Hubble's law
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velocity of recession is directly proportional to distance more distant the galaxy, the faster it moves away from us
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apparent magnitude
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relative brightness as seen from the earth
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absolute magnitude
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relative brightness as seen 10 pc from the star
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critical density
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amount of matter per unit volume space that could create enough gravitational pull so that the universe will continue to expand, yet slow down to a certain point
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how do we know that main sequence stars are made predominantly of hydrogen?
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emission spectrum of the star contains being absorbed by
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cosmic microwave background radiation
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1. it does not come from any particular spot in the sky but rather fills all space 2. radiation detected was remnant of the hot explosion at the beginning of time * When the universe is expanding, it gave off EM waves and these waves have become thin wavelength as the space-time expands to the present time
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asteroid
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rocky substance that orbits around the sun
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red shift
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red-shift is a result of Doppler effect and proves that universe is expanding and galaxies are moving away. therefore universe is not static.
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Newton's model of the universe
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infinite, uniform, static
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stellar parallax method
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if angular position of a star is measured before and after 6 months, the two position will be different relative to a background of a very distant star.
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Olber's paradox
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if universe is infinite, there will be infinite amount of energy. but if the universe is uniform, then each point will receive infinite energy uniformly therefore the sky will be bright.
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comet
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a small body made of mainly ice and dust, orbiting the sun in an elliptical orbit displays atmosphere when close to sun but atmosphere no longer present when far from sun
